Category 1
What are viruses?
Infectious agents that require a host cell to replicate
How many shapes do viral capsids have?
Numerous
What is virulent phage?
Phage that can only replicate via lytic cycle
What happens in a rich nutrient environment?
Protease high and Cro accumulates
What does O and P promote?
Replication of phage genome
What do virus particles contain?
Virus particles (virions) contain:
Nucleic acid genome (DNA or RNA)
Protein capside
Membrane envelope (sometimes)
What is the lytic cycle?
latency
What is bacteriophage lambda?
Temperate phage that infects E. coli
What happens in a poor nutrient environment?
Protease low and cII accumulates
What does cII favor?
lysogeny.
cII is an activator of PI and PRE which promote transcriptions of integrase and cI
What is known about viral genomes?
•DNA or RNA
•Double- or single-stranded
•Sense (+) or antisense (-) (single-stranded genomes)
•Linear or circular
•Encode 2 to 1000’s of genes
What is the lysogenic cycle?
integration
What regulates the choice of lysogeny or lytic growth in bacteriophage lambda?
Genetic switch
What happens in early transcription of phage lambda?
Early transcription from PL and PR promoters makes N and cro proteins
What does cI do?
It is a repressor of PL and PR promoters. REduces transcription of cro
What are the steps of the reproductive cycle for viruses?
Attachment, entry, integration/latency, synthesis of viral components, viral assembly and release
What is prophage?
phage in the genome
What proteins are associated with the lytic cycle in lambda phage? What proteins are associated with lysogenic cycle in lambda phage?
–cII favors lysogenic cycle
–cro favors lytic cycle
What is the importance of N?
N is an anti-terminator transcription proceeds through tL, tR1 and tR2 cII, O, P, Q transcribed
How does bacteria protect against bacteriophage?
Restriction-modification system which cleaves GAATTC sequence. Methylated DNA sequence is unaffected
CRISPR
What happens in the integration/latency stage?
some but not all viruses integrate their genome into the genome of the host cell; others adopt a latent form, in which viral proteins not produced
What is temperate phage?
Phage that can adopt either lysogenic or lytic cycle
What is sensitive to cellular protease?
What does cro favor?
lytic cycle
Cro blocks transcription of PL and PRM promoters but allows low transcription of PR promoter
What is CRISPR
Adaptation- bacteriophage is cut and added to CRISPR as spaces
Expression- Pre-cRNA is processed into crRNAs by endonuclease. Each crRNA has a spacer sequence and baspairs with tracrRNA. crRNA and tracrRNA bind to Cas9
Interference- crRNA targets Cas9 to phage genomic DNA of the same sequence